Natural killer (NK) cells are pivotal in immunosurveillance and hold great potential for immunotherapy due to their ability to target malignant cells. Their low risk of causing graft-versus-host disease (GvHD) post-allogenic transplantation underscores their potential as an off-the shelf cellular therapy tool. Advances in genetic engineering focus on improving NK targeting, persistence, and fitness. However, NK cells pose challenges for lentiviral transduction, which are clinically relevant and safe. In this study, we identified Poloxamer 407 (P407) as a novel transduction enhancer for rhesus macaque (RM) and human NK cells. We found that P407 significantly improved transduction efficiency, achieving up to 60% in expanded RM NK cells, without compromising cell viability or functionality. Additionally, P407 facilitated the expression of anti-CD20 chimeric antigen receptors (CARs) with or without interleukin (IL)-15. In a xenograft mouse model, CAR-IL15 NK cells demonstrated superior anti-tumor activity, and maintained higher clonal diversity tracked by genetic barcoding compared to CAR-NK cells lacking IL-15 in vivo. Additionally, in human NK cells, P407 combined with the TBK1/IKKε inhibitor, BX795, further improved lentivirus-mediated transduction. This study is the first to engineer NK cells from a clinically relevant rhesus macaque model in an adaptive cell therapy context and highlights P407’s potential as a transduction enhancer.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection primarily affects the respiratory system but may induce hematological alterations such as anemia, lymphopenia and thrombocytopenia. Previous studies have reported that SARS-CoV-2 efficiently infects hematopoietic stem and progenitor cells (HSPCs); however, the subsequent effects on hematopoiesis and immune reconstitution have not yet been described. Here we evaluated the pathological effects of infection of umbilical-cord-blood-derived HSPCs with the SARS-CoV-2 Omicron variant pseudovirus (PsV). Transcriptomic analysis of Omicron PsV-infected HSPCs revealed the upregulation of genes involved in inflammation, aging and the NLRP3 inflammasome, suggesting a potential trigger of inflammaging. Omicron PsV-infected HSPCs presented decreased numbers of multipotential progenitors (granulocyte‒erythrocyte‒macrophage‒megakaryocyte colony-forming units) ex vivo and repopulated primitive hematopoietic stem cells (Ki-67−hCD34+ cells) in an HSPC transplantation NOD-scid IL2rγnull mouse model (Omicron mouse). Furthermore, Omicron PsV infection induced myeloid-biased differentiation of HSPCs. Treatment with nanographene oxide, an antiviral agent, partially mitigated the myeloid bias and inflammaging phenotype both in vitro and in vivo. These findings provide insights into the abnormal hematopoietic and immune effects of SARS-CoV-2 infection and highlight potential therapeutic interventions. The coronavirus disease 2019 (COVID-19) pandemic highlights systemic effects of SARS-CoV-2 beyond respiratory symptoms. Researchers investigated its impact on hematopoietic stem and progenitor cells (HSPCs), which produce blood cells, using a pseudovirus mimicking the Omicron variant. Infection caused inflammation and skewed blood production toward myeloid cells (e.g., macrophages), reducing lymphoid cells (e.g., T and B cells). This imbalance mirrors immune disruptions in COVID-19, such as lymphopenia and excessive inflammation. To address these effects, researchers tested nanographene oxide (NGO), a material with antiviral and anti-inflammatory properties. NGO reduced inflammation and partially restored normal blood production without harming HSPCs. Treated cells showed improved immune balance and reduced myeloid bias. These findings reveal how SARS-CoV-2 disrupts blood cell production and suggest NGO’s potential as a therapeutic tool to manage immune imbalances in COVID-19 and other viral infections. Further studies could explore its broader clinical applications. This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author.

ABSTRACT:Immunodeficiency in telomere biology disorders (TBDs) has been described in pediatric patients with severe phenotypes, but is less characterized within the broader TBD spectrum. We collected complete blood counts, lymphocyte subsets, and infection history from 88 consecutive patients with TBD with a median age of 38 years (range, 6-76). Most patients were >18 years old (80/88; 90%) and harbored either a TERT (45%) or TERC germ line mutation (32%). Thirty-two patients (36%) experienced significant infections (opportunistic, recurrent, and/or requiring hospitalization); 47% had lymphopenia, and 3% severe neutropenia. Absolute lymphocyte counts (ALCs) of <0.96 and <1.1 × 103/μL, but not severe neutropenia, were associated with increased infection risk and lower overall survival, respectively. Decreased CD3+ T cells, both CD4+ and CD8+, were associated with bone marrow failure, increased infection risk, and reduced survival. Low CD3+ and CD4+ T cells were associated with solid cancers. Telomere length was shortened across the cohort without correlation with ALC or lymphocyte subsets. In a predominantly adult cohort of TBDs, immunodeficiency was marked by T-cell lymphopenia, possibly a consequence of accelerated aging in the hematopoietic compartment. An ALC cutoff of <1.1 × 103/μL may be a useful biomarker to identify patients with an increased risk of infection, a major cause of death in patients with TBD.

Diamond-Blackfan anemia (DBA) results from germ line haploinsufficiency of 1 of at least 26 distinct ribosomal proteins. Although patients with DBA have hematopoietic stem and progenitor cell defects, the dominant clinical phenotype is severe anemia. In ~60% of patients with DBA, the anemia responds to corticosteroids. However, these responses are often time limited, and steroid-related complications are common, leaving an unmet need for an effective and safe oral therapy. In DBA, ribosomal haploinsufficiency leads to slowed translation and impaired protein synthesis. Globin synthesis is significantly slowed, whereas the production of heme, which requires a small amount of protein because it is synthesized enzymatically, proceeds at a near normal rate. This results in an excess of intracellular heme in early erythroblasts, elevated reactive oxygen species, and other heme-induced toxicity. Bitopertin, an oral competitive inhibitor of glycine import, has been shown to reduce heme synthesis and to have an excellent safety profile in unrelated phase 2 and 3 studies. We reasoned that bitopertin might help balance heme synthesis with globin synthesis and improve erythropoiesis in patients with DBA. Our observations in samples from patients with DBA, CD34+ cells engineered to downregulate RPS19, and a murine DBA model support this concept, justify ongoing clinical studies, and provide insight into optimal trial design.

Hematopoietic stem cells (HSC) with multilineage potential are critical for T cell reconstitution after allogeneic hematopoietic cell transplantation (allo-HCT). The Kitlo HSC subset is enriched for multipotential precursors, but their T cell potential remains poorly characterized. Using a preclinical allo-HCT mouse model, we demonstrate that Kitlo HSCs provide superior thymic recovery and T cell reconstitution, resulting in improved immune responses to post-transplant infection. Kitlo HSCs with augmented bone marrow (BM) lymphopoiesis mitigate age-associated thymic alterations and enhance T cell recovery in middle-aged mice. Mechanistically, chromatin profiling reveals Kitlo HSCs exhibiting higher activity of lymphoid-specifying transcription factors, such as, ZBTB1. Zbtb1 deletion diminishes HSC engraftment and T cell potential; by contrast, reinstating Zbtb1 in megakaryocytic-biased Kithi HSCs rescues hematopoietic engraftment and T cell potential in vitro and in vivo. Furthermore, age-associated decline in Kitlo HSCs is associated with diminished T lymphopoietic potential in aged BM precursors; meanwhile, Kitlo HSCs in aged mice maintain enhanced lymphoid potential, but their per-cell capacity is diminished. Lastly, we observe an analogous human BM KITlo HSC subset with enhanced lymphoid potential. Our results thus uncover an age-related epigenetic regulation of lymphoid-competent Kitlo HSCs for T cell reconstitution.

Abstract The US Food and Drug Administration announcement in November 2023 regarding reports of the occurrence of secondary T-cell lymphomas in patients receiving chimeric antigen receptor T cells (CAR-Ts) for B-cell malignancies resulted in widespread concern among patients, clinicians, and scientists. Little information relevant to assessing causality, most importantly whether CAR retroviral or lentiviral vector genomic insertions contribute to oncogenesis, was initially available. However, since that time, several publications have provided clinical and molecular details on 3 cases showing clonal CAR vector insertions in tumor cells but without firm evidence these insertions played any role in oncogenic transformation. In addition, several other cases have been reported without vector detected in tumor cells. In addition, epidemiologic analyses as well as institutional long-term CAR-T recipient cohort studies provide important additional information suggesting the risk of T-cell lymphomas after CAR-T therapies is extremely low. This review will provide a summary of information available to date, as well as review relevant prior research suggesting a low susceptibility of mature T cells to insertional oncogenesis and documenting the almost complete lack of T-cell transformation after natural HIV infection. Alternative factors that may predispose patients treated with CAR-Ts to secondary hematologic malignancies, including immune dysfunction and clonal hematopoiesis, are discussed, and likely play a greater role than insertional mutagenesis in secondary malignancies after CAR therapies.

For precise genome editing via CRISPR/homology-directed repair (HDR), effective and safe editing of long-term engrafting hematopoietic stem cells (LT-HSCs) is required. The impact of HDR on true LT-HSC clonal dynamics in a relevant large animal model has not been studied. To track the output and clonality of HDR-edited cells and to provide a comparison to lentivirally transduced HSCs in vivo, we developed a competitive rhesus macaque (RM) autologous transplantation model, co-infusing HSCs transduced with a barcoded GFP-expressing lentiviral vector (LV) and HDR edited at the CD33 locus. CRISPR/HDR-edited cells showed a two-log decrease by 2 months following transplantation, with little improvement via p53 inhibition, in comparison to minimal loss of LV-transduced cells long term. HDR long-term clonality was oligoclonal in contrast to highly polyclonal LV-transduced HSCs. These results suggest marked clinically relevant differences in the impact of current genetic modification approaches on HSCs.

Background Mesenchymal stem cells (MSCs) play important roles in tissue homeostasis by providing a supportive microenvironmental niche for the hematopoietic system. Cigarette smoking induces systemic abnormalities, including an impeded recovery process after hematopoietic stem cell transplantation. However, the role of cigarette smoking-mediated alterations in MSC niche function have not been investigated.Methods In the present study, we investigated whether exposure to cigarette smoking extract (CSE) disrupts the hematopoietic niche function of MSCs, and pathways impacted. To investigate the effects on bone marrow (BM)-derived MSCs and support of hematopoietic stem and progenitor cells (HSPCs), mice were repeatedly infused with the CSE named 3R4F, and hematopoietic stem and progenitor cells (HSPCs) supporting function was determined. The impact of 3R4F on MSCs at cellular level were screened by bulk-RNA sequencing and subsequently validated through qRT-PCR. Specific inhibitors were treated to verify the ROS or NLRP3-specific effects, and the cells were then transplanted into the animal model or subjected to coculture with HSPCs.Results Both direct ex vivo and systemic in vivo MSC exposure to 3R4F resulted in impaired engraftment in a humanized mouse model. Furthermore, transcriptomic profile analysis showed significantly upregulated signaling pathways related to reactive oxygen species (ROS), inflammation, and aging in 3R4F-treated MSCs. Notably, ingenuity pathway analysis revealed the activation of NLRP3 inflammasome signaling pathway in 3R4F-treated MSCs, and pretreatment with the NLRP3 inhibitor MCC950 rescued the HSPC-supporting ability of 3R4F-treated MSCs.Conclusion In conclusion, these findings indicate that exposure to CSE reduces HSPCs supportive function of MSCs by inducing robust ROS production and subsequent NLRP3 activation.

Abstract Telomere biology disorders (TBDs), caused by pathogenic germ line variants in telomere-related genes, present with multiorgan disease and a predisposition to cancer. Clonal hematopoiesis (CH) as a marker of cancer development and survival in TBDs is poorly understood. Here, we characterized the clonal landscape of a large cohort of 207 patients with TBD with a broad range of age and phenotype. CH occurred predominantly in symptomatic patients and in signature genes typically associated with cancers: PPM1D, POT1, TERT promoter (TERTp), U2AF1S34, and/or TP53. Chromosome 1q gain (Chr1q+) was the commonest karyotypic abnormality. Clinically, multiorgan involvement and CH in TERTp, TP53, and splicing factor genes were associated with poorer overall survival. Chr1q+ and splicing factor or TP53 mutations significantly increased the risk of hematologic malignancies, regardless of clonal burden. Chr1q+ and U2AF1S34 mutated clones were premalignant events associated with the secondary acquisition of mutations in genes related to hematologic malignancies. Similar to the known effects of Chr1q+ and TP53-CH, functional studies demonstrated that U2AF1S34 mutations primarily compensated for aberrant upregulation of TP53 and interferon pathways in telomere-dysfunctional hematopoietic stem cells, highlighting the TP53 pathway as a canonical route of malignancy in TBD. In contrast, somatic POT1/PPM1D/TERTp mutations had distinct trajectories unrelated to cancer development. With implications beyond TBD, our data show that telomere dysfunction is a strong selective pressure for CH. In TBD, CH is a poor prognostic marker associated with worse overall survival. The identification of key regulatory pathways that drive clonal transformation in TBD allows for the identification of patients at a higher risk of cancer development.

Haematopoietic stem and progenitor cell (HSPC) autologous gene therapies are promising treatment for a variety of blood disorders. Investigation of the long-term HSPC clonal dynamics and other measures of safety and durability following lentiviral-mediated gene therapies in predictive models are crucial for assessing risks and benefits in order to inform decisions regarding wider utilization. We established an autologous lentivirally barcoded HSPC transplantation model in rhesus macaque (RM), a model offering insights into haematopoiesis and gene therapies with direct relevance to human. Healthy young adult RMs underwent total body irradiation, followed by transplantation of autologous HSPCs transduced with a lentiviral vector containing a diverse genetic barcode library, uniquely labelling individual HSPCs and their progeny. With up to 131 months of follow-up, we now report quantitative clonal dynamics, characterizing the number, diversity, stability and lineage bias of hundreds of thousands of HSPC clones tracked in five RMs. We documented long-term stable and multi-lineage output from a highly polyclonal pool of HSPCs. Clonal succession after stable haematopoietic reconstitution was minimal. There was no evidence for accelerated acquisition of acquired somatic mutations following autologous lentivirally transduced HSPC transplantation. Our results provide relevant insights into long-term HSPC behaviours in vivo following transplantation and gene therapies.

Immunodeficiency in telomere biology disorders (TBDs) is often observed in patients with severe phenotypes presenting at a young age, as in dyskeratosis congenita. The immune system of adult TBD patients, including risk of infection and correlation with survival has not been well characterized. We reviewed the clinical records of 88 TBD patients (median age [range] = 35 [5-76]; 93% with a known germline mutation) followed at NHLBI since 2002. Significant infections were defined as opportunistic, recurrent (two or more severe infections in one year, three or more respiratory infections in one year, or the need for antibiotics for two months per year), or infections that required hospitalization. Longitudinal data of blood counts and T, B, and NK (TBNK) cell immunophenotyping were available for 88 and 55 patients, respectively. Lymphopenia and neutropenia were defined as ≤ 1.2 cell/mL and 0.5 cell/mL. Immunodeficiency was defined by CD8 ≤ 178 cell/µL, CD4 ≤ 334 cells/µL, or CD19 ≤ 60 cells/µL. In this adult cohort, 32/88 (36%) had a clinically significant infection history: 8/32 (25%) opportunistic, 16/32 (50%) recurrent, and 21/32 (65%) requiring hospitalization. Of 88 patients, 41 were lymphopenic and only 3 were neutropenic. Of 55 patients with available data for TBNK subsets, 29 were immunodeficient. Twenty-three had decreased CD3 counts, including 22 patients with decreased CD4 count and 13 patients with decreased CD8 count. B lymphopenia was observed in 16 patients. Median age was similar between groups with normal and abnormal blood counts and TBNK subsets. Lymphopenia but not neutropenia correlated with infections. Using decision tree analysis, absolute lymphocyte counts (ALC) <1.1 and <0.96 cell/µL segregated patients with worse overall survival (OS) and at increased risk of infections, respectively. CD3 lymphopenia (both CD4 and CD8) correlated with infections requiring hospitalization and opportunistic infections, both of which also associated with poorer OS. B lymphopenia only correlated with recurrent infections and did not impact OS. Potential underlying mechanisms associated with T lymphopenia in TBDs are increased cell apoptosis due to excessive telomere shortening and an accelerated aged hematopoiesis characterized by decreased T CD4/CD8 ratio and myeloid bias of hematopoietic stem and progenitor cells (HSPC). Telomere length (TL) of T cells was similarly shortened across the entire cohort in comparison to age-matched controls, regardless of ALC and TBNK levels. TBNK immunophenotyping showed that 38/55 (69%) had a decreased CD4/CD8 ratio, a finding further validated in 6 patients by single-cell proteogenomics (scDNA) of peripheral immune subsets. In comparison to young (n=1) and older (n=1) controls, TBD patients had decreased naïve T CD4+ and CD8+ subsets, and accumulation of effector and memory cells, consistent with an aged immune system. Increased frequencies of naïve T, NK and B cells were observed in 2/6 patients, both with PPM1D or TERTp somatic mutations. In the entire cohort, clonal hematopoiesis (CH) in MDS-related genes (particularly in U2AF1S34 and TP53 but not PPM1D) associated with low ALC and CD3/4/8 levels (p < 0.05). scRNA-seq of HSCs from patients with germline TERT/TERC (n=2) without CH showed the lymphoid and myeloid progenitor pool (LMPP) intrinsically biased towards myeloid differentiation, with increased expression of myeloid markers in comparison to LMPP from age-matched controls. Although MDS-related mutations are known to be associated with a myeloid biased hematopoiesis, differential expression of U2AF1S34 vs. U2AF1wild-type LMPP by scRNA-seq were equivalent. In conclusion, immunodeficiency in adult TBDs is characterized by T lymphopenia and likely consequent to accelerated aged hematopoiesis. Low ALC and T CD3/4/8 levels may be useful as biomarkers of increased risk of clinically significant infections and poor OS.

B cells are an attractive platform for engineering to produce protein-based biologics absent in genetic disorders, and potentially for the treatment of metabolic diseases and cancer. As part of pre-clinical development of B cell medicines, we demonstrate a method to collect, ex vivo expand, differentiate, radioactively label, and track adoptively transferred non-human primate (NHP) B cells. These cells underwent 10- to 15-fold expansion, initiated IgG class switching, and differentiated into antibody-secreting cells. Zirconium-89-oxine-labeled cells were infused into autologous donors without any preconditioning and tracked by PET/CT imaging. Within 24 h of infusion, 20% of the initial dose homed to the bone marrow and spleen and distributed stably and equally between the two. Interestingly, approximately half of the dose homed to the liver. Image analysis of the bone marrow demonstrated inhomogeneous distribution of the cells. The subjects experienced no clinically significant side effects or laboratory abnormalities. A second infusion of B cells into one of the subjects resulted in an almost identical distribution of cells, suggesting possibly a non-limiting engraftment niche and feasibility of repeated infusions. This work supports the NHP as a valuable model to assess the potential of B cell medicines as potential treatment for human diseases.

Telomeres as the protective ends of linear chromosomes, are synthesized by the enzyme telomerase (TERT). Critically short telomeres essentially contribute to aging-related diseases and are associated with a broad spectrum of disorders known as telomeropathies. In cardiomyocytes, telomere length is strongly correlated with cardiomyopathies but it remains ambiguous whether short telomeres are the cause or the result of the disease. In this study, we employed an inducible CRISPRi human induced pluripotent stem cell (hiPSC) line to silence TERT expression enabling the generation of hiPSCs and hiPSC-derived cardiomyocytes with long and short telomeres. Reduced telomerase activity and shorter telomere lengths of hiPSCs induced global transcriptomic changes associated with cardiac developmental pathways. Consequently, the differentiation potential towards cardiomyocytes was strongly impaired and single cell RNA sequencing revealed a shift towards a more smooth muscle cell like identity in the cells with the shortest telomeres. Poor cardiomyocyte function and increased sensitivity to stress directly correlated with the extent of telomere shortening. Collectively our data demonstrates a TERT dependent cardiomyogenic differentiation defect, highlighting the CRISPRi TERT hiPSCs model as a powerful platform to study the mechanisms and consequences of short telomeres in the heart and also in the context of telomeropathies.

Patients with severe aplastic anemia (SAA) are at high risk of morbidity and mortality due to severe infections. We aimed to characterize the role of granulocyte transfusions (GT) in SAA. Primary outcomes were survival after the first GT, including overall survival (OS) at last follow up, survival to discharge, and receipt of a hematopoietic stem cell transplant (HSCT) Secondary outcomes included evaluation of clinical response at 7 and 30 days after initiation of GT, using a clinical scoring system incorporating microbiological and radiographic response. Twenty-eight SAA patients underwent 30 GT courses with a per-dose median of 1.28x109 granulocytes/kilogram (range, 0.45-4.52x109). OS from initial GT to median last follow up (551 days) was 50%, with 39% (11/28) alive at last follow up. Sixty-four percent (18/28) of all patients survived to hospital discharge. Patients with a complete or partial response, or stable infection, at 30 days had significantly better OS compared to non-responders (P=0.0004). Eighty-six percent (18/21) of patients awaiting HSCT during GT underwent a transplant and 62% (13/21) survived to post-HSCT discharge. Sex, type of infection, and percentage of days with absolute neutrophil count >0.2x109/L during the course of GT were not predictive of survival (P=0.52, P=0.7 and P=0.28, respectively). Nine of 28 (32%) patients developed new or increased human leukocyte antigen alloimmunization during their GT course. GT in SAA may have an impact on survival in those patients with improvement or stabilization of their underlying infection. Alloimmunization can occur and OS in this population remains poor, but GT may be a useful tool to bridge patients to curative treatment with HSCT.